What are the causes of pharyngitis?

Usually a virus (about 90% of cases). Pharyngitis may also be caused by a bacteria such as Group A Streptococcus. It is not possible to clinically differentiate between a viral and streptococcal pharyngitis.

It is not possible clinically to distinguish viral from bacterial pharyngitis.

Infectious mononucleosis due to infection with the Epstein-Barr virus may also cause a pharyngitis, often with a membrane. Diphtheria is a rare cause of membranous pharyngitis. Bacterial infection can be diagnosed if a throat swab is taken for culture.